How to adjust contrast on watt meters?

[ebike11]

Hi all!
I got a new GT power watt meter, but the figures on the screen are very faint and can barely see them
Is there any way to make the contrast darker?

Sorry if this was covered before
Thanks!!

 

[dnmun]

put in a dark room.

 

[ebike11]

Still doesnt help

 

[ebike11]

Anyone have this problem before as well?

 

[Gregory]

Well it uses a standard 1602 LCD display so check the resistor/pot on pin 3 (maybe 2 to 3K ohm?).

You can try using a 10K pot to test if it dims.

 

[Gregory]

Yes I believe the contrast is pin 3..where would I get that kind of pot switch?
I never ever seen or used one in my life

Thanks for your time!!

Hi ebike11, I don't have the GT meter, and can't find an internal pic.
I'd open it and measure what resistance is connected to pin #3 then try reduce it by either putting in a pot or a resistor in parallel to drop resistance. It may not solve it, but it is a place to start.

 

[ebike11]

Well it uses a standard 1602 LCD display so check the resistor/pot on pin 3 (maybe 2 to 3K ohm?).

You can try using a 10K pot to test if it dims.

Hi
I put the neg. voltmeter prong on the neg. of the wattmeter lead and pos. prong to the 3rd pin after opening up the back
It reads 0.86 ohms. I hope that's accurate Its a first for me to test such a device

 

[dnmun]

nope, the reading means nothing. it is not gonna be possible for you to actually change the contrast without taking the meter apart and rewiring the circuits that are now just copper traces on a pcb in between those two layers. if you spread the layers apart by folding at the pins the thing will break because the black plastic alignment shields will cause the pcb to tear apart before you get the two layers apart. if you can desolder each of the pins separately so you can then separate the two layers then you could experiment with the surface mount resistors on the power board side of the wattmeter. but then you would need to have the schematic and understand how to read an electrical schematic, and if he wants to send you a schematic to look at then he would.

 

[ebike11]

oh I came across a possible fix, looks to me an easy solder job if its just 3 wires

http://www.youtube.com/watch?v=kMP7lXtiqDc

 

[dnmun]

yes, that would work. pin 1 is ground, pin 2 is Vcc, pin 3 is the reference voltage.

looking at the power board of mine i have torn apart, which i think is an old turnigy, but they are all the same almost.

between pin 2 and ground on the pcb is a '116' labeled surface mount and another in series in the divider is labeled 01B which i do not know how to decode. i measured it with my meter and got 777 ohms and the one labeled 116 is 735 ohms.

Vcc is 3.3V so that should give you an idea of the voltage range where the contrast feedback is ranging. so what they are doing in that video is putting the trimpot in parallel with 1,2,3 with the wiper on pin 3.

i will try to find a 10k trimpot and see if i can do something similar since i have a meter i have open here already.

 

[ebike11]

yes, that would work. pin 1 is ground, pin 2 is Vcc, pin 3 is the reference voltage.

looking at the power board of mine i have torn apart, which i think is an old turnigy, but they are all the same almost.

between pin 2 and ground on the pcb is a '116' labeled surface mount and another in series in the divider is labeled 01B which i do not know how to decode. i measured it with my meter and got 777 ohms and the one labeled 116 is 735 ohms.

Vcc is 3.3V so that should give you an idea of the voltage range where the contrast feedback is ranging. so what they are doing in that video is putting the trimpot in parallel with 1,2,3 with the wiper on pin 3.

i will try to find a 10k trimpot and see if i can do something similar since i have a meter i have open here already.

ok...let us know the results

 

[dnmun]

i am working on another project right now. i have been doinng range tests on my little ZENN car and got it up to 96 miles yesterday but i realized i needed to add a voltmeter so i am repairing an old single cell, cell phone charger to use to provide a current source to the meter driven off the battery leads.

but for this problem, 777+735=1512R, so i think you could just put the 10k trimpot with the wiper tied to one end, between pin 2 and pin three or between pin 3 and pin 1 and adjusting to see if either side increases the contrast. but use a high value resistor, or trimpot and if you find that one side allows you to adjust the contrast to your satisfaction, then pull the trimpot off and measure the resistance and then for a permanent solution, one could solder a surface mount resistor across the space between the pins. i will get to it yet.

 

[ebike11]

ok ill have to order a 10k pot on ebay

 

[Gregory]

Good find on the youtube video! That illustrates it perfectly.

I was thinking like pins #1,2,3 in this pic if it helps clarify things.

Good luck.
Greg

 

[Gregory]

Hi there how are you?
We had posted in a thread awhile back about the contrast with the GT Power watt meter here:

I recently got a 10 pot
http://www.ebay.ca/itm/2-x-10K-OHM-TRIMPOT-TRIMMER-POTENTIOMETER-3296W-3296-/250852988345

It has 3 prongs and 3 wires are needed to run to the watt meter.

I was wondering, would you know, does it mater which prongs on the connect to the VSS/VDD/V0 (that is what is labelled on my meter), a certain order?
Or can I run any combination from the pot to the meter?

Thanks for your time!!!

Vss is negative, VDD is positive, they should go to either outside pins on the pot. Doesn't matter which - just one combination will make it increase clockwise the other combination will be the reverse.

The wiper pin on the pot is normally the middle pin, and goes to V0. That will make it a voltage divider. You can measure the resistance with the pot turned a few turns, from pin 1 to 3 and that should be approx 10K, just to confirm pin 2 is the wiper.